Adding a module wide logger, and setup logic.

We have found that having logs would improve our workflow, this commit simply adds a Lhm wide logger, which is just a
simple ruby Logger instance, it must be configured once before the first call to Lhm.logger, via the Lhm.logger_params
accessor, probably from a Rails initializer.

Adding the most basic logger statements

Explicitly setting logger formatter to nil to get the default format

Update lhm_spec.rb

Update lhm_spec.rb

Update lhm_spec.rb
Merge pull request #62 from Shopify/pr_logging

Adding a module wide logger, and setup logic.

Conflicts:
	.gitignore
	lib/lhm.rb
	lib/lhm/invoker.rb
:scissors:

Also add Copyright